A number sequence is a list of numbers arranged in a specific order, following a particular pattern or rule. Each number in the sequence is called a term, and the position of each term is usually indicated by its index. For example, the sequence 2, 4, 6, 8 increases by 2 each time, making it an arithmetic sequence. Number sequences can be finite, having a limited number of terms, or infinite, continuing indefinitely. They can also be defined by various rules, such as Fibonacci numbers, where each term is the sum of the two preceding ones. Understanding these sequences is essential in mathematics and various real-world applications.